The present invention relates to the production of advanced ceramics using supercritical fluid technology.
Silicon nitride is a hard, high strength, light weight structural ceramic with useful thermal shock resistance and toughness. Many uses have been identified in automobile drivetrains, air conditioning compressors, bearings, cutting tools, and chemical process systems.
The high thermal conductivity of aluminum nitride makes it useful for electronic substrates.
Powder metallurgy, high temperature reaction bonding, and sol gel methods for making advanced ceramics are well known. U.S. Pat. No. 4,961,913 to Sullivan describes a method using supercritical fluids to react and extract silicon containing solids or organometallic halides to form bonded ceramic materials. U.S. Pat. No. 5,011,819 to Leibovitz describes a method using supercritical fluids to extract byproducts from materials to form pure powders with controlled stoichiometry for making 1-2-3 superconductive ceramics. U.S. Pat. No. 4,552,786 to Berneburg et al. describes a method using supercritical fluids to transport organometallic polymers into a fiber architecture preform followed by pyrolysis. As should be self-evident from the description hereinafter, the present invention distinguishes from the teachings of these patents.
Chemical vapor reaction between silicon monosulfide vapor and gaseous ammonia at temperatures ranging from about 1250.degree. C. to 1500.degree. C. is described by Forsyth in U.S. Pat. No. 3,211,527 as means of making silicon nitride. U.S. Pat. No. 4,552,740 to Morgan et al. describes a method of making silicon nitride by first reacting silicon metal with hydrogen sulfide at 800.degree. C. to 1000.degree. C. followed by reaction of silicon disulfide with gaseous ammonia between 800.degree. C. to 1200.degree. C. Silicon carbide can also be made by substituting an amine gas for ammonia. Again, the present invention distinguishes from the teachings of these references. The low temperatures of the reactions disclosed herein are not taught in the prior art.